Generally, a bicycle speed change device includes a front speed change device mounted to the front side of the bicycle and a rear speed change device mounted at the rear side of the same.
The conventional front side speed change device, as disclosed in Japanese Patent Laid Open-Gazette No. Sho 62-99,293, is constructed such that (1) a cylindrical fixing member is provided around the crank shaft, (2) a plurality of sun gears are independently rotatably supported around the fixing member, (3) planetary gears engageable with the sun gears are supported to a disc-like carrier fixed to the crank arm, (4) a chain gear having internal teeth engageable with the planetary gears is rotatably provided, (5) a plurality of lock pawls are provided between the respective sun gears and the fixing member to be independently swingable to lock or unlock the rotation of the sun gears, and (6) a cylindrical control member having bores for receiving therein the tips of the lock pawls is provided, so that the control member is rotated to forcibly actuate each lock pawl in the unlocking direction.
The conventional speed change device provides for manual operation of the control member to actuate the lock pawls in the unlocking direction, so that when the bicycle speed is manually changed in the condition in which the chain gear is driven by a treading force, the speed change operation via the control member is very heavy, thereby creating a problem in that the speed change operation is hard to carry out.
In particular, in a case in which the treading force is transmitted from the crank arm to the chain gear through the carrier and planetary gears to thereby drive the chain gear in the state where rotations of the sun gears are restrained by the lock pawls, since a reaction force caused by rotation of each planetary gear acts on the engaging portion of the lock pawl with the sun gear, even when the control member is operated, it is difficult to actuate the lock pawls in the unlocking direction, with the result that, when the treading force drives the chain gear, it is very hard to carry out the speed control function.